The present invention relates to a non-prism type light wave distance measuring method and a non-prism type light wave distance measuring system.
A distance measuring system using a light wave is a system for projecting a distance measuring light to an object to be measured and for measuring a distance to the object to be measured from a measuring position by receiving a reflection light reflected by the object to be measured. In general, the light wave distance measuring systems divide into two types. One of the two types is a light wave distance measuring system which requires a reflection prism (corner cube) as the object to be measured. The other is a non-prism type light wave distance measuring system without using the reflection prism. The non-prism type light wave distance measuring system projects a distance measuring light directly to an object such as a building, etc. and measures the distance by a reflection light from the object to be measured. In both types of the system, the schematical arrangement and the principle of distance measurement are approximately the same.
Referring to FIG. 4, description will be given on an essential portion of the distance measuring system.
The distance measuring system comprises an optical unit 1 for projecting and receiving a distance measuring light, a driving circuit 3 for driving a light emitting source 2, a photodetection circuit 4 for converting the received distance measuring light to an electric signal, and a distance calculating circuit 5 for calculating a distance based on a signal from the photodetection circuit 4. The optical unit 1 for projecting and receiving the distance measuring light comprises the light emitting source 2 for emitting a distance measuring light 6, a projecting optical system 8 for projecting the distance measuring light 6 from the light emitting source 2 to an object to be measured 7 such as a building, etc., a photodetection optical system 9 for guiding a reflected distance measuring light 6′ from the object to be measured 7, a photodetection unit 10 for receiving the reflected distance measuring light 6′ guided by the photodetection optical system 9, and a timing circuit 11 for sending a clock signal to the distance calculating circuit 5.
An optical path changeover chopper (not shown) is provided at the middle of an optical path of the distance measuring light 6 and an optical path of a reference light 18 (to be described later) so that the optical pathes are selectively intercepted.
Under the condition that the optical path of the reference light 18 is intercepted by the optical path changeover chopper, the distance measuring light (pulsed laser light or modulated laser light) 6 emitted from the light emitting source (e.g. a semiconductor laser) 2 is deflected by a reflection mirror 14 via a projection side half-mirror 12 and an optical fiber 13 and the distance measuring light 6 is directed toward an objective lens 15 of the projecting optical system 8. After being turned to approximately a parallel luminous flux by the objective lens 15, the distance measuring light 6 is projected toward the object to be measured 7 via the objective lens 15. The reflected distance measuring light 6′ reflected by the object to be measured 7 is directed again toward the objective lens 15. Being directed toward the objective lens 15, the reflected distance measuring light 6′ is converged by the objective lens 15. The reflected distance measuring light 6′ is then deflected by the reflection mirror 14, and passes through an optical fiber 16 and a photodetection side half-mirror 17. An image is formed on the photodetection unit 10, and the reflected distance measuring light 6′ is received by the photodetection unit 10.
Furthermore, under the condition that the optical path of the distance measuring light 6 is intercepted by the optical path changeover chopper, the distance measuring light 6 emitted from the light emitting source 2 is split and reflected by the projection side half-mirror 12. The distance measuring light 6 as a reference light 18 is then reflected and deflected by the photodetection side half-mirror 17, and the reference light 18 enters the photodetection unit 10.
At the photodetection unit 10, the reflected distance measuring light 6′ or the reference light 18 is received. At an electrical unit (not shown), the reflected distance measuring light 6′ and the reference light 18 thus received are converted to electric signals. Based on the electric signals, the distance calculating circuit 5 calculates a distance to the object to be measured 7.
Referring to FIG. 5, description will be given now on operation in case the distance is calculated according to a photodetection signal of the reflected distance measuring light 6′ and the photodetection signal of the reference light 18.
Under the condition that the optical path of the reference light 18 is intercepted by the optical path changeover chopper, the light emitting source 2 is driven by the driving circuit 3, and the distance measuring light is emitted as a pulsed light. A pulse signal synchronized with the light emission is inputted to the distance calculating circuit 5 as a light emission pulse P1. Being projected via the objective lens 15, the distance measuring light 6 is reflected by the object to be measured 7 and the distance measuring light 6 is turned to the reflected distance measuring light 6′. The reflected distance measuring light 6′ enters the photodetection unit 10 via the photodetection optical system 9. A photodetection signal from the photodetection unit 10 is processed as necessary (e.g. amplification, etc.) at the photodetection circuit 4, and the photodetection circuit 4 produces a photodetection pulse R1 and the photodetection pulse R1 is inputted to the distance calculating circuit 5.
The distance calculating circuit 5 counts clock number between the light emission pulse P1 and the photodetection pulse R1. That is, the distance calculating circuit 5 calculates the time. The clock number is multiplied by light velocity, and approximate distance is calculated. Further, based on phase difference between the light emission pulse P1 and the photodetection pulse R1, a precise measured distance is calculated. By combining the precise measurement with the rough measurement using clock number, a distance to the object to be measured 7 is calculated.
Under the condition that the optical path of the distance measuring light 6 is intercepted by the optical path changeover chopper, the light emitting source 2 is driven by the driving circuit 3, and a pulsed light is emitted. The pulsed light is inputted to the photodetection unit 10 as the reference light 18 via the projection side half-mirror 12 and the photodetection side half-mirror 17.
The distance calculating circuit 5 measures the optical path of the internal reference light based on the light emission pulse P1 and the photodetection pulse R1. The measurement circuit includes an error. The error can be cancelled by subtracting the measurement value in the optical path of the internal reference light from the measurement value of the object to be measured 7 determined by the distance measuring light 6.
From the measurement value of the object to be measured 7, the measurement value of the optical path of the internal reference light determined by the reference light 18 is subtracted. By adding a correction value, a precise measured distance is obtained.
Next, as the situations to perform the distance measurement, there are the following cases, for example,: a case where the distance to the object to be measured is measured via a glass, or a case where there is a metal net between the distance measuring system and the object to be measured, etc. In this case, there is a reflection light from an object not to be measured such as the glass, the metal net, etc. Thus, the photodetection unit 10 outputs the photodetection pulse R1 based on the reflected distance measuring light 6′ and also outputs the photodetection pulse R2 based on the reflection light from the object not to be measured as shown in FIG. 6. In this respect, when the distance calculating circuit 5 counts the clock number, it is not possible to judge which of the clock number of the photodetection pulse R1 or the clock number of the photodetection pulse R2 should be counted. If the clock number of the photodetection pulse R2 is counted, it is erroneous measurement. Or two measurement values are generated, and this causes erroneous operation.
The light wave distance measuring instrument is disclosed, in JP-A-5-232230 and JP-A-2001-153655.